U.S. Pat. No. 4,994,534 ('534) and U.S. Pat. application Ser. No. 08/029,821 are concerned with the introduction of fluidization aids into a polymerization reactor to avoid the agglomeration of sticky polymers. In the drawing of '534, the fluidization aid, referred to as inert particulate material, which can be, for example, carbon black, silica, or clay, is introduced into the polymerization reactor through a feeder vessel into transport lines in which the solids are carried along into the reactor by an inert gas.
Typically, the feeder vessel is operated under high pressure, and the transport lines and the reactor are operated under a relatively lower pressure. The inert particulate material is loaded into the high pressure vessel at atmospheric pressure. Then, the vessel is pressurized, usually with an inert gas such as nitrogen. When the discharge valve of the high pressure vessel is opened, the inert particulate material is forced out of the high pressure vessel through conduits or supply lines to a receiving vessel, which can be a polymerization reactor, all operated at a lower pressure. Such a procedure has its limitations when dealing with an inert particulate material, which is in the form of a cohesive fine powder, e.g., powders having an average particle size of about 150 or less microns. Examples of cohesive fine powders are soft carbon beads having the aforementioned particle size.
Generally, cohesive fine powders have very poor permeability and, thus, are easily packed. If the high pressure gas is injected directly into the bed of cohesive fine powder in the high pressure vessel, the force of the high pressure gas causes the powder to form a "bridge" inside the high pressure vessel and then pack. Once the bridge is formed, the feeding process from the high pressure vessel to the reactor fails.
To prevent the cohesive fine powder from being packed inside the high pressure vessel, the gas is permitted to expand and reduce its pressure before it contacts and compresses the bed of cohesive fine powder. In this way, the force of the gas is spread evenly across the bed, and the formation of a bridge with consequent packing is reduced, but still a problem.
One solution to this problem was to provide a hollow aeration cone inside of the high pressure vessel. This aeration cone evolved into a double cone, and was eventually improved by adding perforations to the lower end of the bottom cone, i.e., close to the apex of the inverted cone. However, even with this improved device, the combination of high pressure and the cohesive fine powder served to plug up the discharge valve of the high pressure (above about 50 psia) vessel. The blocked discharge valve, in turn, caused a bridge to be formed and the cohesive fine powder to pack thus nullifying the effect of the perforated double aeration cone.